This invention relates to a method of communicating with each of a plurality of detonators in a blasting system.
An important step in carrying out a blasting event is to establish that each detonator which should be included in a blasting system is present and is functional. This can be done, for example, by means of a roll call process wherein an interrogating signal is sent repeatedly from a control device. Each detonator, in turn, responds to the interrogating signal and thereby notifies the control device that the detonator is present. Status information can also be presented to the control device.
U.S. Pat. No. 7,848,078 describes a method for polling a plurality of detonators. Each detonator, in an interconnected array of detonators, is interrogated to reply in a time slot that is associated with a unique anti-collision response time stored in the detonator. The successful implementation of this technique requires that each detonator includes a unique timing device, such as an oscillator, which must be calibrated to ensure that the replies from the various detonators are separated, in time, from one another and do not overlap. The accuracy of an oscillator is, however, dependent on various factors including temperature and, in order to eliminate the effects of oscillator drift, each of the oscillators must be calibrated shortly before the detonators are polled.
Different approaches to the situation are described in U.S. Pat. Nos. 7,533,613 and 7,971,531. The latter case requires a blasting machine to be preloaded with detonator identifiers. Other art in the field includes U.S. Pat. Nos. 7,870,825, 7,322,293, and 7,017,494.
An object of the present invention is to provide a polling technique which does not require oscillator calibration nor pre-loading of identity numbers into a blasting machine, and which avoids “collisions” between signals from responding detonators.